1. Field of the Invention
The present invention relates to a demultiplexer and transport decoder employing the demultiplexer.
2. Discussion of Related Art
There have been proposed a lot of methods for transmission/reception format for digital processed picture and audio data between media. One of them is MPEG 2 system part proposed by MPEG 2, which makes picture-compressed and audio-compressed data in a format which can be easily used, to transmit and receive the data between media. In the transmission and reception of video data and audio data, the video data and audio data are encoded, compressed, and multiplexed by MPEG transport encoder, to be transmitted. The multiplexed stream is received, and demultiplexed by MPEG transport decoder, and the video data and audio data are decoded by MPEG video decoder and audio decoder respectively, to be supplied to a user.
FIG. 1A is a block diagram of a conventional MPEG decoder. The configuration and operation of the conventional MPEG decoder is explained with reference to FIG. 1A. The MPEG encoder includes; first and second encoders 10 and 11 for encoding input video data and audio data, to output video bit stream and audio bit stream, respectively, first and second packetizers 12 and 13 for packetizing the video bit stream and audio bit stream sent from first and second encoders 10 and 11; and a multiplexer 14 for multiplexing the packetized bit streams, to make one bit stream, and store or transmit it.
When video data is received, first encoder 10 compresses/codes the video data, to convert is into MPEG video bit stream. When audio data is received, second encoder 11 compresses/codes the audio data, to convert it into MPEG audio bit stream. The MPEG video bit stream converted by first encoder 10 is sent to first packetizer 12, to be packetized in a proper length and output to multiplexer 14. The audio bit stream compressed by second encoder 11 is sent to second packetizer 13, to be packetized in a proper length and output to multiplexer 14.
The video and audio streams are multiplexed by multiplexer, 14, to be converted into one bit stream, and stored or transmitted through a channel. Multiplexer 14, the transport multiplexer, not only receives MPEG video bit stream and audio bit stream but multiplexed compressed/coded video stored or transmitted through a channel. Multiplexer 14, the transport multiplexer, not only receives MPEG video bit stream and audio bit stream but multiplexes compressed/coded video stream and audio stream other than the MPEG video and audio bit streams, to store them as one bit stream and transmit it through a channel. To decode a program consisting of video data and audio data and provide a user with it, a desired bit stream must be selected. For this, it is required that a specific identification (ID) is given to each bit stream, and information on the ID is additionally provided. Accordingly, the additional data is sent to the transport stream by multiplexer 14, to be stored or transmitted. The configuration of the transport bit stream is shown in FIG. 1B. In FIG. 1B, reference numeral H represents headers of the transport bit stream, P.sub.1 A and P.sub.2 A represent audio signal sections, P.sub.1 V and P.sub.2 V represent video signal sections, and hatched portion represents headers of packetized element stream (PEG).
FIG. 2A illustrates a conventional typical MPEG transport decoder. The streams stored in multiplexer 14 shown in FIG. 1A or transmitted through a channel, that is, the streams transmitted through the airwaves, or stored is a CD-ROM and then reproduced, are applied to a first decoder 20 shown in FIG. 2A. First decoder 20 tunes and demodulates a signal input and audio stream, and outputs them to second and third decoders 23 and 24, respectively.
Second decoder 23 decodes the video stream, to reproduce a video signal according to an output timing signal supplied from a clock controller 22. Third decoder 24 decodes the audio stream, to reproduce an audio signal according to the output timing control signal applied from clock controller 22. The video and audio signals output from second and third decoders 23 and 24 are MPEG signals which do not include the above-described headers as shown in FIG. 2C. These signals are not used for recording but used for displaying. In other words, demultiplexer 21 outputs the audio data and video data having no headers, decodes and displays them. Thus, when the data having no header is stored in a recording medium, it is impossible to reproduce the data from the medium.
That is, data is output from demultiplexer 21 in the form of packet, and multiple packets are divided into audio packet and video packet depending on their header information. Accordingly, because the conventional transport decoders output only audio data and video data which do not include header information, when the data is recorded in a recording medium, and then reproduced, it is impossible to confirm if the reproduced data is the audio packet or video packet. Thus, correct decoding cannot be performed. To enable the transport decoder to output both audio and video data for display as shown in FIG. 2C and audio video data including headers for recording as shown in FIG. 2B, it requires two transport decoders 31 and 32 shown in FIG. 2D.
First transport decoder 31 outputs the data for displaying, and second transport decoder 32 outputs the data including headers for recording. The data for displaying is displayed through a display 33, and data for recording is recorded in a recording medium 34. Here, clock controller 22 controls timing between second decoder 23, third decoder 24, demultiplexer 21, to adjust lip sync or decoding rate between video data and audio data. Due to the broad and complicated transport stream of the conventional transport decoder, there are developing lots of program type transport demultiplexers. However, these demultiplexers can be variously applied according to programs, but their operation speed is deteriorated. Furthermore, the demultiplexers require additional cores other than necessary logics, increasing their sizes.